The results of this study indicate that decidualization of the uterine stroma is necessary for maintaining the expression of IGF-I and IGFBP-4 mRNA in the mouse uterus both during and after implantation of the embryo. Our data reveal that before implantation, the maternal hormones of pregnancy support IGF-I and IGFBP-4 mRNA expression. Beyond gestational Day 4, however, decidualization of the uterine stroma, either artificially induced or naturally induced by an implanting embryo, is sufficient for maintaining the expression of these two genes. Thus, the presence of specific embryo factors is not required for IGF-I and IGFBP-4 expression in the periimplantation mouse uterus. Initial in situ hybridization studies were conducted to compare the expression patterns of IGFBP-4 and IGF-I mRNAs in the periimplantation mouse uterus. Our experiments revealed that, like IGFBP-4 mRNA, IGF-I mRNA is expressed in a cell-specific and temporally dynamic manner in the mouse uterus during the periimplantation period.
These experiments demonstrated a rapid induction of IGF-I mRNA between Days 5 and 6 of gestation, followed by a decline in IGF-I mRNA after the establishment of embryo implantation. However, we were unable to reproduce the pattern of IGF-I expression originally shown by Kapur et al. in a previously published paper. In the current study, IGF-I mRNA was first detected by reverse transcription-polymerase chain reaction (RT-PCR) analysis of uterine RNA extracts on Day 2 of pregnancy (data not shown) and then by in situ hybridization on Day 3 of pregnancy. ventolin inhalers
In contrast, Kapur et al., using in situ hybridization, were able to detect a faint IGF-I signal on gestational Day 2. On Day 6 of pregnancy, we detected an intense ring of IGF-I mRNA signal in uterine stromal cells adjacent to the myometrium, while Kapur et al. reported a diffuse distribution of IGF-I mRNA throughout the deciduum, with more intense signal in the primary decidual zone. Although differences between the IGF-I riboprobes used and the level of sensitivity of the techniques employed may account for differences between these two studies, it is unclear why the distribution patterns of IGF-I appear to be dissimilar.